Cannot send E-Mail to others in your company or domain after server change

Cannot send E-Mail to others in your company or domain, after changing E-Mail Hosts or upgrading from Exchange server 2003, to 2008:

Go to your "Local" Profile at following location:

if Vista\7:
C:\ (if default Win install):\Users\\AppData\Local\Microsoft\Outlook

if XP: %UserProfile%\Local Settings\Application Data\Microsoft\Outlook.

Backup all your *.oab [Offline Address Book] files.
After backup remove all your *.oab files, from your profile \AppData\Local…

Start Microsoft Outlook, it will rebuild the files and your problem should be resolved